Stereoscopic three-dimensional (stereo 3-D) devices continue to be popular in a multitude of applications. If safe and effective 3-D content is to be developed, a better understanding of how the visual system responds to stereoscopic media needs to be established. Technological advances have improved stereo media, but problems remain. One of the more fundamental problems with conventional stereoscopic 3-D displays is termed the ‘vergence-accommodation conflict’. This refers to the inappropriate stimulus to the eye’s focusing response (accommodation) at the screen surface while the image points are presented stereoscopically nearer and farther than the screen. This causes a mismatch or conflict between the stimuli to accommodation and vergence. The vergence and accommodation response systems are neurally coupled (Fincham & Walton, 1957; Martens and Ogle, 1959), which means that changes in vergence drives changes in accommodation and vice versa. Therefore a clear, stereoscopic percept requires decoupling these normally coupled responses. This PhD thesis investigates several aspects of how vergence-accommodation conflict affects perception of stereo 3-D. We first explored the effectiveness, and practicality, of a proposed solution to vergence-accommodation conflicts known as multiple-focal-planes displays (Chapter 3). Unfortunately, these displays are more suited to individual viewing, such as gaming or laparoscopic surgery in medicine, however, using such displays is infeasible for situations such as cinema and television. We therefore also investigated several aspects of tolerance of perception of stereo 3-D to vergence-accommodation conflicts in conventional displays. We measured how an individual’s stereo acuity varies as a function of vergenceaccommodation conflict, and whether viewing such stimuli causes an after-effect on subsequent ‘real-world’ viewing (without conflict; Chapter 4). We also examined several factors that might predict individual differences in perception of stereo 3-D with vergenceaccommodation conflicts, most notably age-related changes in the ability to accommodate (presbyopia; Chapter 5). Our findings suggest that multiple-focal-plane displays can be used to create stereo images that are comparable to real-world images while matching the vergence- and accommodation-specified distances. For the instances where these displays cannot be used, vergence-accommodation conflict causes adverse effects on stereo performance. In chapters 4 and 5, we found that there are large individual differences in stereo performance when viewing 3-D stereo content. However, generally, as the vergenceaccommodation conflict increases, so too do the negative effects on stereo performance. In chapter 5, we found that the ophthalmological factors of the audience, including degree of presbyopia and phoria can act as an indicator for individual tolerance to viewing stereo 3-D images on conventional displays. These findings should contribute both to the development and specification of future stereo 3-D displays, and to developing content for conventional displays that better match the properties of the user’s visual system.